The below-identified Patent document 1 discloses an electric linear motion actuator configured to convert the rotation of a rotor shaft of an electric motor into the linear motion of a driven member supported by a motion converting mechanism to be movable in the axial direction.
The electric linear motion actuator of Patent document 1 includes a rotary shaft configured to be rotated by an electric motor, an outer ring member formed on its inner diameter surface with a helical rib, a plurality of planetary rollers provided between the rotary shaft and the outer ring member, and each formed in the outer diameter surface thereof with a helical groove or circumferential grooves, and a carrier supported to be rotatable about the rotary shaft, and rotatably supporting the planetary rollers, the electric linear motion actuator being configured such that when the rotary shaft rotates, due to the frictional contact of the planetary rollers with the rotary shaft, the planetary rollers rotate about their axes while revolving around the rotary shaft so that the outer ring member and the carrier axially linearly move relative to each other due to the engagement of the helical rib of the outer ring member in the helical grooves or circumferential grooves of the planetary rollers.
The electric linear motion actuator of Japanese Unexamined Patent Application Publication No. 2010-90959 further includes a pair of disks constituting the carrier, and thrust roller bearings each mounted between one of the planetary rollers and the surface of one of the disks that is opposed to the one of the planetary rollers such that the thrust loads applied to the planetary rollers are supported by the respective thrust roller bearings, thereby reducing the rotational resistance of the planetary rollers while rotating about their axes.
Since the electric linear motion actuator of Japanese Unexamined Patent Application Publication No. 2010-90959 is configured to axially linearly move the outer ring member and the carrier relative to each other due to the engagement of the helical rib of the outer ring member in the helical grooves or circumferential grooves of the planetary rollers, a force increasing function can be obtained without separately providing a reduction mechanism such as planetary gears, and thus this actuator is suitable for an electromechanical brake system in which a linear motion stroke is relatively small.
The electric linear motion actuator of Japanese Unexamined Patent Application Publication No. 2010-90959 includes thrust roller bearings rotatably supporting the respective planetary rollers, and each comprising a single raceway disk and a thrust roller and retainer assembly which is the combination of a plurality of roller elements and a retainer radially retaining the roller elements. Since it is necessary to separately mount the thrust roller and retainer assembly and the single raceway disk to each roller shaft rotatably supporting the corresponding planetary roller, it takes time to assemble the carrier. Also, misplacements and/or inadvertent omissions of components of such thrust roller bearings tend to occur.
The above electric linear motion actuator further includes a plurality of pillar members retaining the pair of disks at a predetermined distance from each other, and each formed in the end surfaces thereof with threaded holes. The carrier is assembled by threadedly engaging bolts in the threaded holes of the disks through bolt insertion holes of the disks, and fastening the bolts. As a result thereof, it takes a lot of time to assemble the carrier. Therefore, a measure needs to be taken to easily assemble the carrier.
Also, since it is necessary to form bolt insertion holes and threaded holes by machining, costs are high. Therefore, a measure needs to be taken to reduce costs.
It is an object of the present invention to easily assemble a carrier supporting planetary rollers.